Among other things, an apparatus includes a wheelchair control device sensitive to motion and adapted to attach to a user’s head, and includes a wheelchair interface device in communication with the wheelchair control device and adapted to manipulate a control system of a motorized wheelchair in response to communication from the wheelchair control device. An apparatus for generating wavelength-stabilized light is formed of a light-emitting device, an external cavity and at least one external mirror. The noise reduction fairing 12 may include a wrap-around fairing which, when the landing gear 10 is in its fully deployed position, wraps around the landing gear 10 and extends along the majority of the length of a landing gear leg 11.